[Elecraft] K3 Voltmeter calibration ...

Tue Nov 24 19:55:34 EST 2015

As I responded to to Mark off list, I know the REF ADC calibration and
had already performed it *before* asking for assistance here.  The
voltage display was off by more than 0.5 V prior to performing REF ADC.
The remaining the error is still unacceptably high at more than 0.2 
Volts when a simple DVM has significantly greater accuracy.

I *still* seem to recall a calibration procedure for voltage similar to
that for FP, PA, etc. during the initial assembly and test of this K3.
It seems inconceivable that such a calibration process would not be
present since the "12V" sense point follows at least D6 if not D6, Q2,
RFC40 and R36 which in total would introduce a substantial fraction of
a volt offset from the voltage at the APP and provided to the KPA3.

73,

   ... Joe, W4TV

On 11/24/2015 6:32 PM, Mark E. Musick wrote:
> I sent Joe K3 manual REV D6 from early in 2010.
> On page 53 of that manual it has the following description for ADC REF and
> how to calibrate it.
>
> ADC REF
>
> Allows calibration of the voltage reference used by the K3 to measure and
> display
> certain values, such as the rig's supply voltage. (Optional.) First,
> disconnect
> anything attached to the ACC jack. Next, locate the ADC REF menu entry. It
> will
> initially show 5.00 volts as the reference voltage. Using a DMM set to DC
> volts,
> measure the actual voltage at pin 2 of the ACC jack. This must be done while
> the
> ADC REF parameter is being displayed. (Note: The (-) probe of the DMM
> should go to the K3's chassis ground, e.g. at the GROUND lug.) Finally, use
> VFO
> A to set the ADC REF menu parameter to what you measured at pin 2.
>
> So you need to set ADC REF to the voltage on pin 2 of the ACC jack. NOT what
> is at the APP connection on the RF board.
>
> 73,
>
> Mark Musick, WB9CIF
>
> -----Original Message-----
> From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Brian
> & Cyndi
> Sent: Tuesday, November 24, 2015 11:19 PM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3 Voltmeter calibration ...
>
> And the info below is what I found in Fred Cady's book on the K3. There is
> no other "calibration" for voltage in that book.
>
> Until Don Wilhelm or Wayne Burdick chimes in,  I suspect there may not be
> any other adjustment available.
>
> 73,
> Brian, W6FVI
>
> On 11/24/2015 1:49 PM, Joe Subich, W4TV wrote:
>>
>> I've already set ADC REF as documented in the manual.  The Voltage is
>> still off.  There should be a procedure to set the voltage as there
>> was when I assembled this K3 (s/n 1450) several years ago.
>> Unfortunately, I can no longer find it in the current Owner's Manual
>> or Assembly Manual.
>>
>> 73,
>>
>>    ... Joe, W4TV
>>
>>
>> On 11/24/2015 4:01 PM, Brian & Cyndi wrote:
>>> Joe, if you just want to make the K3's voltmeter match your "known good"
>>> reference meter, you need to adjust the "ADC REF" value.
>>>
>>> Go into the CONFIG menu, set Tech mode "On", then go to the "ADC REF"
>>> setting.  Note what it is before changing anything, in case this
>>> adjustment affects anything else adversely.  Adjust the ADC REF value
>>> to cause the voltmeter display to read the value you want. You will
>>> need to go in and out of the menu display to see the results (kinda
> clumsy).
>>>
>>> Again, this adjustment may affect other measurements, so an accurate
>>> K3 voltmeter may not be that important after all.
>>>
>>> 73,
>>> Brian, W6FVI
>>>
>>> On 11/24/2015 9:32 AM, Joe Subich, W4TV wrote:
>>>>
>>>> It matters not if there is a series diode.  The Voltmeter should be
>>>> calibrated to the input power.  I remember that being the case when
>>>> I assembled my first K3.
>>>>
>>>> 73,
>>>>
>>>>     ... Joe, W4TV
>>>>
>>>>
>>>> On 11/24/2015 11:02 AM, Michael Blake wrote:
>>>>> Joe, is there not at least one diode junction or solid state switch
>>>>> in series with the input power inside the K3?
>>>>>
>>>>> Michael Blake - K9JRI
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>> On Nov 24, 2015, at 10:06 AM, Joe Subich, W4TV <lists at subich.com>
>>>>>> wrote:
>>>>>>
>>>>>>
>>>>>> OK, I'm sure I am overlooking something simple but I can not find
>>>>>> (or remember) how to calibrate the voltage display in the K3.
>>>>>>
>>>>>> I had to repair one of my Astron RS-35A power supplies for the
>>>>>> first time in 30 years (one of the diodes shorted) and when I put
>>>>>> it back on line I decided to double check the K3 Volts display
>>>>>> against the actual output of the supply.  The K3 is reading about
>>>>>> 0.2V less than the supply voltage.
>>>>>>
>>>>>> I've been over both the K3 Owner's Manual and the K3 Assembly
>>>>>> Instructions but can't find any reference to calibrating the
>>>>>> voltage display.
>>>>>>
>>>>>> 73,
>>>>>>
>>>>>>     ... Joe, W4TV
>>>>>>
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